Moments before stepping to the podium Tuesday night to acknowledge that he would be the first black candidate nominated by a major party for president of the United States, Barack Obama and his wife, Michelle, knocked knuckles.

It was a tiny gesture so cool, so tight, so loving and so right, that it seemed to encapsulate both the satisfaction of the moment and the new cultural trajectory of American politics.

“Barack and Michelle were giving each other some ‘dap,”’ says Mark Anthony Neal, a professor of black popular culture at Duke University. “I was watching the speech with my wife and she saw ‘the dap’ and said, ‘Do you see that? A bunch of folks must be wondering what that means.”

It spoke volumes — about the Obama’s relationship with one another, about his and their relationship with the American people who decide in November whether to move them into the White House, and about America’s relationship to black culture, the nation’s test kitchen for cooking up what’s next in popular taste, style and expression.

“It was a way for them to have a very private moment in an immensely public spot and at a moment when everyone was watching them,” Neal says. “It’s something I do every day with my oldest daughter, who is 9. It’s a way to express that kind of love and affection for each other without the hug and kiss fathers normally do with their daughters. …

“I think it speaks to one of the elements of why Obama has been successful. What you’ve seen in the last 20, 25 years is really the mainstreaming of black popular culture, so Obama is a product of what I’ll call multiracial blackness,” Neal says. “So many folks are now consuming black culture as if it were their own.”

To wit: NBC Nightly News anchor Brian Williams, who on Wednesday asked Obama about the dap, noting that Michelle had “tried to give her husband a fist pound the way a lot of Americans do, the way a lot of couples do. The only problem it’s an inside move shared in front of 17-and-a-half thousand people in the arena and millions watching at home.”

Obama’s answer: “It captured what I love about my wife. There’s an irreverence about her and sense that for all the hoopla, that I’m her husband and sometimes we’ll do silly things and yet she’s proud of me and she gives me some credit once in a while that I actually pull some things off.”

Or as “cee cee,” posting on Afrobella put it, “The pound to me meant: ‘we did it! through thick and thin, side by side … ”’

It also signaled that, for all they have sacrificed over the course of the campaign — including membership in the church where they were wed and their children baptized — the Obamas are still black and still cool, still comfortable in who they are.

Of course, as “Town” asked in a posting on Jack and Jill Politics, “Which one will claim that Barack and Michelle were using some secret black power fist gang signal to call blacks worldwide to arms? Sean Hannity? Geraldine Ferraro? Pat Buchanan?”

In fact, Neal says, the dap probably does trace its early origins to the black power salute of the 1960s.

But it morphed into what it is today — lateral instead of vertical — in the intersection of hip-hop and the National Basketball Association in the 1980s. In the years since, it has become familiar beyond the black world to many Americans under the age of 50 — especially to anyone glued to a television as professional athletes congratulate each other on exceptional performance.

Black people and those under 50 — a demographic that in the last few months has come to be known by another name: Obama voters.